1. Field of the Invention:
The invention relates to a technique for the controlled transmission of radiant energy. More particularly, the invention is directed to an apparatus and systems in which the transmission of a flux of light or other radiant energy as it passes through an appropriate medium is controlled by a second flux of radiant energy, or the evanescent field thereof, such that transistor-like gain is achieved. Contemplated applications of the apparatus of this invention include fiber optics, optical integrated circuits, macroscopic optical devices for communications, sensing and control, optical computing, image processing, etc.
2. Description of the Prior Art:
A significant part of modern technology is concerned with apparatus and systems in which radiant energy is in some way altered during transmission through a medium. Communications systems, for example, may make use of a carrier wavelength of radiation energy which is somehow altered in analog or digital manner so as to represent intelligence. An ever-increasing part of technology depends upon communications systems of increasing sophistication which again generally depend upon a variation of some characteristic of energy with complex computations being the cumulative result of a multiplicity of such variations, possibly in discrete control elements. Such systems have, in the past, depended on relatively low frequency energy, perhaps DC, while later developments make increasing use of higher and higher frequency energy. This trend has gained impetus through the invention and development of the laser oscillator, variations of which may now produce CW or pulsed radiation at wavelengths from the far infrared through the visible spectrum and into the ultraviolet.
It is known to use induced absorption within a medium for one or more specified wavelengths of energy. Induced absorption permits operations such as those of switching and modulating, for example, for the interposition of variations representing information. U.S. Pat. No. 4,209,690 assigned to Bell Telephone Laboratories discloses an apparatus which can operate as an extremely rapid shutter, a switch, a modulator or a pulsed sharpener.
However, in the design of fiber or integrated optical circuits there remains a need for an optical amplifying system which can perform in a manner analogous to the transistor in an electronic circuit. While optical amplification based on photon multiplication via stimulated emission or parametric amplification is known, it is an object of this invention to disclose an optical amplifier which utilizes excited state absorption to produce a variable optical resistance or absorption. The result is a device characterized by transistor-like gain in switching capabilities.
It is another object of this invention to provide an optical transistor in which the photons from a control flux of radiant energy modulate the intensity of a signal flux of radiant energy in such a way that a change of one photon in the control flux causes a change of more than one photon in the signal flux.
It is yet another object of this invention to provide an optical transistor which utilizes a first and a second control flux of radiant energy such that a one photon increase in the first control flux causes a decrease of more than one photon in the signal flux, while a one photon increase in the second control flux causes an increase of more than one photon in the signal flux.